Every sixth to eighth European intensive care unit patient suffers from an underlying malignant disease. A large proportion of these patients present with cancer-related complications. This review explains why the prognosis of critically ill cancer patients has improved substantially over the last decades and which risk factors are of prognostic importance. Furthermore, the main reasons for intensive care unit admission – acute respiratory failure and septic complications – are discussed with regard to diagnostic and therapeutic specifics. In addition, we discuss potential intensive care unit admission criteria with respect to cancer prognosis. The successful management of critically ill cancer patients requires a close collaboration of intensivists with hematologists, oncologists and colleagues from other disciplines, such as infectious disease specialists, microbiologists, radiologists, surgeons, pharmacists, and others.